Water is our most basic commodity. In Vermont, we expect drinking water to be inexpensive, plentiful, and safe. Occasionally, however, drinking water supplies become contaminated due to a nearby failed septic system or other forms of pollution. In 2000, Vermonters learned of another kind of contamination.

Unlike polluted flood water or hazardous waste spills, this odorless, tasteless contaminant was hundreds of millions of years in the making. Concealed deep within Vermont's ancient geology are long-lived radioactive elements which have tarnished local drinking water sources.

Levels of naturally occurring radioactivity above Vermont's drinking water standard were discovered in the wells of several public community water systems and a number of private homes within the Champlain Valley. While all rocks are radioactive to some degree, levels of radioactivity are usually low. Deeper bedrock wells typically have higher levels than wells in sand and gravel deposits. As groundwater slowly moves through the bedrock fractures of an aquifer, radioactive elements mix with the water and go into solution with the groundwater.

To measure radiation levels, operators of public community water systems take an initial water sample to test for gross alpha, an indicator of the overall level of radiation in the water. If the results indicate high levels, additional radiation measurements, often for radium, are taken. Both gross alpha and radium can cause health problems if exposures are at sufficient doses for a significant duration. However, the immediate health risks from drinking water with levels of radioactivity are low. The U.S. Environmental Protection Agency estimates that 70 years of drinking water at the maximum contaminant level adds one fatal cancer death to an exposed population of 10,000 -- and there are ways to decrease the risk even further. These include finding an alternative water source or blending the affected water with potable water from another source. Treatment options also exist, but unfortunately these processes concentrate the radioactivity, creating waste disposal problems.

The first line of defense against drinking water contamination is awareness, which for many Vermonters is available through their public community water systems' annual consumer confidence reports (CCR). Each CCR lists the highest detected level for each regulated contaminant with respect to water quality standards. In addition, a CCR provides health effect information for dozens of contaminants, including lead, arsenic, mercury, and benzene. Private well owners and all homeowners can have their water tested for radiation along with other contaminants at the Vermont Health Department Laboratory.

While the likelihood of drilling a well that supplies highly radioactive water and subsequently contracting cancer is low, it should not be dismissed. Nor should we perpetuate the myth that unadulterated sources of water are to be found anywhere and everywhere in Vermont. Drinking water from above and below ground is subject to natural and human-made contamination. Surface water is exposed to animal waste, algae, organic matter, and run-off containing petroleum, pesticides, and salts. Even the most remote mountain stream or hillside spring can contain Giardia or bacteria. Disinfection of surface water prior to drinking is necessary.

Mercury

Forty-six states, including Vermont, have fish consumption advisories warning their citizens to limit the number of fish they eat due to mercury contamination. The Vermont Department of Health recently identified several reservoirs (Comerford and Moore Reservoirs on the Connecticut River and all Deerfield River reservoirs) with mercury levels elevated to the point that women of childbearing age and children younger than seven should not eat any fish from these waters. The most toxic form of mercury found in fish is methylmercury, a toxin created largely through naturally occurring processes in surface waters. Methylmercury has particularly strong toxic effects on fetal and childhood brain development.

In Vermont, mercury comes almost entirely from atmospheric sources, the result of coal burning in Midwestern states and local waste incineration and fuel oil combustion. The Agency of Natural Resources is working at the international level to curb mercury emissions from industrial areas. Vermonters can help by recycling products that contain mercury, such as old thermostats and fever thermometers (many pharmacies offer a thermometer trade-in program), and by not using backyard burn barrels, which is also illegal.

Concentrations of mercury in Vermont's lakes and rivers are neither high enough to harm swimmers nor in most cases serious enough to affect the water's suitability for treatment and subsequent drinking. Methylmercury does bioaccumulate, however, meaning it increases in concentration as it moves up the food chain. Long-lived carnivorous fish can display elevated mercury levels, and therefore pose a danger to people who eat them. Fish-eating waterfowl, including sensitive species such as common loons and bald eagles, are at risk of accumulating dangerous levels of mercury. Twelve percent of Vermont's breeding loons have sufficiently high mercury exposure that their ability to reproduce is impaired or precluded. In New Hampshire and Maine, the percentages of loons at similar risk are even higher.

The Department of Environmental Conservation has commenced a research project with several partners seeking to understand how mercury moves through a lake chemically, how it transforms into methylmercury, and what makes fish and waterfowl more susceptible to mercury accumulation in certain lakes. This information will be used to refine the fish consumption advisories so they reflect the conditions in individual lakes. The Department is also initiating a collaborative study of mercury in reservoir systems.

For further information, the Vermont Department of Health Fish Advisory is available online (http://healthvermont.gov/enviro/fish_alert/fish_alert.aspx) and by calling 1-800-439-8550. A summary of the Advisory Committee on Mercury Pollution's activities can be found online at www.mercvt.org.